ATRP is a versatile, controlled/living polymerization process. ATRP has been described by Matyjaszewski in U.S. Pat. Nos. 5,763,548 and 5,807,937 and in the Journal of Americal Chemical Society, vol. 117, page 5614 (1995), as well as in ACS Symposium Series 768, and Handbook of Radical Polymerization, Wiley: Hoboken 2002, Matyjaszewski, K., and Davis, T. P., editors (Handbook of Radical Polymerization), specifically Chapter 11, all hereby incorporated by reference. In controlled polymerizations such as ATRP, fast initiation and low termination rates result in the preparation of well-defined polymers with low polydispersity. A variety of initiators, typically alkyl halides, have been used successfully in ATRP. As used herein, an “ATRP initiator” is a chemical compound or functionalized particle comprising radically transferable atom or group, such as a halogen or a transferable (pseudo)halogen. Many different types of halogenated compounds may be used as potential ATRP initiators. ATRP can be conducted in bulk or in solution using solvents selected to dissolve the formed copolymer.
Living/controlled polymerizations typically, but not necessarily, comprise a relatively low stationary concentration of propagating chain ends in relation to dormant chain ends. When the chain is in the dormant state, the chain end comprises a transferable atom or group. The dormant chain end may be converted to a propagating chain end by loss or weakening of the bond of the transferable atom or group in a reaction with an added transition metal complex.
In ATRP, radically polymerizable monomers are polymerized in the presence of a transition metal catalyst. For a list of radically polymerizable monomers, see U.S. Pat. No. 5,763,548, hereby incorporated by reference. Though the details of the complex mechanism are not fully understood, it is believed that the transition metal catalyst participates in a redox reaction with at least one of an ATRP initiator and a dormant polymer chain. Suitable transition metal catalysts comprise a transition metal and a ligand coordinated to the transition metal. Typically, the transition metal is one of copper, iron, rhodium, nickel, cobalt, palladium, or ruthenium. In some embodiments, the transition metal catalyst comprises a copper halide, and preferably the copper halide in the activator state is one of Cu(I)Br or Cu(I)Cl.
There are basically four types of polymerization in aqueous dispersed media: suspension polymerization, emulsion polymerizations, mini emulsion polymerization and microemulsion polymerizations. The classification of the process depends on the size of the oil droplets and micelles in the aqueous phase and the composition of the individual oil droplets and micelles. Controlled/living emulsion polymerizations are economically and environmentally important for industrial production of commercially viable products. An initial step towards expanding the scope of ATRP to aqueous dispersed media was ATRP in an emulsion polymerization system. [U.S. Pat. No. 6,121,371 and Gaynor, S. G.; Qiu, J.; Matyjaszewski, K. Macromolecules 1998, 31, 5951-5954; and Chambard, G.; De Man, P.; Klumperman, B. Macromol. Symp. 2000, 150, 45-51.] While some level of control was attained the system behaved in many ways like a suspension polymerization. In this process, the catalyst was initially dissolved in the monomers prior to forming the emulsion. Therefore, the majority of the catalyst was present in the monomer droplets and not the micelles. Only a limited portion of the catalyst could be transported through the aqueous phase from droplets to micelles. Therefore, polymerization occurred throughout the dispersed oil phase.
There has been significant research in miniemulsion polymerization processes for aqueous biphasic ATRP, and other controlled/living radical polymerizations (CRP) processes such as Nitroxide Mediated Polymerization (NMP) and Reversible Addition Fragmentation Transfer (RAFT). See, for example, U.S. Pat. No. 6,759,491, U.S. application Ser. No. 10/271,025 and PCT/US05/007265. Miniemulsion polymerization process overcame the problem of mass transport of monomers and/or catalyst components through the aqueous phase thereby providing significantly improved control over the polymerization their suspension polymerizations. Such improved control may allow preparation of stable latexes comprising polymeric materials of controlled molecular composition and functionality. Homopolymers [Li, M.; Min, K.; Matyjaszewski, K. Macromolecules 2004, 37, 2106-2112.], block copolymers [Li, M.; Jahed, N. M.; Min, K.; Matyjaszewski, K. Macromolecules 2004, 37, 2434-2441; and Min, K.; Gao, H.; Matyjaszewski, K. J. Am. Chem. Soc. 2005, 127, 3825-3830.], and gradient copolymers [Min, K.; Li, M.; Matyjaszewski, K. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 3616.] have been successfully prepared in a miniemulsion polymerization system by ATRP.
U.S. Pat. No. 6,624,262, hereby cited and incorporated by reference in its entirety, describes a controlled radical polymerization process, such as ATRP, that allows preparation of materials where aspects of composition, topology or architecture and functionality can be predetermined in addition to the polymerization exhibiting first-order kinetics behavior, predeterminable degree of polymerization, narrow molecular weight distribution, and long-lived polymer chains. Understanding the scope and meaning of this language is important since prior art microemulsion polymerization procedures discussed below use similar language to that employed in ATRP but do not, and indeed cannot, prepare similar polymers.
There is a need therefore to develop a robust controlled radical polymerization process that can be conducted in dispersed aqueous media that can control all the desired molecular and process parameters. There is also a need for an aqueous dispersed polymerization process that can be conducted with a commercially viable concentration of reagents in commercially viable equipment at a commercially viable scale.